Proceedings of The Physiological Society

University of Oxford (2011) Proc Physiol Soc 23, PC75

Poster Communications

Oxygen uptake kinetics during moderate intensity cycling in obese individuals

C. Kiely1, E. O Connor1, M. Egana1

1. Trinity College Dublin, Dublin 2, Ireland.


Peak oxygen uptake (VO2peak) is reduced in obese individuals in comparison with lean individuals1,2. In addition the dynamic response of oxygen update during the initial period of exercise is slowed in obese adolescents during sub-maximal cycle exercise at specific percentages of VO2peak3. However, as yet no studies have examined VO2 kinetic responses during exercise intensities performed relative to ventilatory threshold (VT) and/or in obese adults. Accordingly the purpose of this study was to investigate the VO2 kinetic response during moderate intensity cycle exercise performed relative to VT in obese participants. To explore underlying mechanisms of potential differences, cardiac output (CO) responses were also measured. Fourteen obese (mean±SD, age: 55.1±5.8 yr, BMI: 32.1±1.7 kg.m-2) (7 men, 7 women) and fourteen control (age: 50.8±12.0 yr, BMI: 23.3±1.6 kg.m-2) (7 men, 7 women) individuals completed a graded cycle test to volitional exhaustion for the determination of VO2peak and VT. On a separate occasion subjects completed four 6-min bouts of constant load cycle exercise at 80% VT for the determination of VO2 kinetics. The dynamics of the VO2 response were established by fitting a bi-exponential function to the VO2 data (averaged from 4 bouts). An indicator of the rate of change for the total VO2 response was obtained by calculating the mean response time (MRT), which is the time taken to reach 63% of the total amplitude from baseline to end-exercise. CO was measured at rest and during exercise at two time points (30 s and 240 s) during two further 6-min bouts using a closed circuit inert gas rebreathing technique. Values are means ± SD compared using an unpaired Student’s t-test. Peak VO2 was significantly lower in obese (24.1±5.2) than control (30.6±8.0) subjects (P<0.05) but VO2 (ml.kg-1.m-1) at VT was similar between obese (18.3±5.8) and controls (22.3±6.6). There were no differences between obese and control subjects in the time constant of phase II (s) of the VO2 kinetic response (40.4±11.2 vs. 36.6±10.0 respectively), MRT (s) (50.3±9.9 vs. 46.5±10.8 respectively) or the time constant (s) of the heart rate kinetic response (63.7±24.8 vs. 58.7±10.6 respectively. Similar responses were observed between obese and control groups in relation to CO (L.min-1) during exercise at 30 s (9.4±2.8 vs. 9.1±2.7, respectively) and 240 s (11.1±3.0 vs. 11.4±3.2 respectively). In addition the rate of adaptation in CO from rest to steady state exercise (% steady state CO) was not different between obese (70.0±14.4) and control (62.4±13.5) groups. The results suggest that despite a lower maximal aerobic capacity, sub-maximal exercise performance in grade 1 obesity (range of BMI: 30-35) seems to be preserved. This was shown by similar VO2 responses at VT and similar dynamic responses of VO2 and CO during moderate cycle exercise in obese and lean groups.

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